Memory is one type of integrated circuitry, and is used in computer systems for storing data. Integrated memory is usually fabricated in one or more arrays of individual memory cells. The memory cells might be volatile, semi-volatile, or nonvolatile. Nonvolatile memory cells can store data for extended periods of time, and in some instances can store data in the absence of power. Non-volatile memory is conventionally specified to be memory having a retention time of at least about 10 years. Volatile memory dissipates, and is therefore refreshed/rewritten to maintain data storage. Volatile memory may have a retention time of milliseconds, or less.
The memory cells are configured to retain or store memory in at least two different selectable states. In a binary system, the states are considered as either a “0” or a “1”. In other systems, at least some individual memory cells may be configured to store more than two levels or states of information.
Integrated circuit fabrication continues to strive to produce smaller and denser integrated circuits. There is a continuing effort to reduce the number of components in individual devices because such can reduce the size of finished constructions, and can simplify processing. The smallest and simplest memory cell will likely be comprised of two electrodes having a programmable material, and possibly a selection device (such as a diode or ovonic threshold switch), received between them.
Suitable programmable materials have two or more selectable memory states to enable storing of information by an individual memory cell. The reading of the cell comprises determination of which of the states the programmable material is in, and the writing of information to the cell comprises placing the programmable material in a predetermined state. Some programmable materials retain a memory state in the absence of refresh, and thus may be incorporated into nonvolatile memory cells.
Phase change materials, such as ovonic memory materials (for instance, various chalcogenides), are being considered for utilization as programmable materials in memory cells. The phase change materials transform from one phase to another through application of appropriate electrical stimulus, with each phase corresponding to a different memory state. The ovonic memory materials may be utilized in combination with selection devices, such as diodes or ovonic threshold switches.
An example prior art memory array 1 comprising chalcogenic phase change memory elements is shown in FIG. 1. The memory array 1 comprises a plurality of memory cells 2, each including a memory element 3 of the phase change type and a selection device 4. The memory cells 2 are interposed at cross-points between rows 6 (also called wordlines or access lines) and columns 5 (also called bitlines or sense lines). In each memory cell 2, the memory element 3 has a first terminal connected to a wordline 6 and a second terminal connected to a selection element 4. The selection element 4 has a second terminal connected a bitline 5.
A problem that may be encountered in the utilization of ovonic materials as memory elements and/or as selection devices is that it can be difficult to adhere ovonic material to various other materials. Accordingly, delamination of ovonic material from adjacent materials may occur. Such delamination can be detrimental to memory cell performance, and in some cases may lead to failure of memory cells. It would be desirable to develop improved memory cells having better adherence of ovonic materials to adjacent materials.